Not local eco-stuff... also, implied in your post is the idea that
A. may have been more optimal for tree to tree flight than modern
birds, and birds sacrificed that to obtain long-distance flight.
Highly doubtful, right?

Not only highly doubtful, but not what I was trying to imply. It may
simply have been that there was no particular selective advantage for
the development of modern bird flight mechanisms over the method used
by Archaeopteryx with respect to short tree to tree flights, but as
the modern mechanisms improved and rendered birds capable of other
types of flight, the selective advantage improved as well.